Magnetic grabs for lifting, turning, and transporting heavy bodies composed of magnetically attractable material, in particular, slabs, coils, or other magnetically attractable heavy loads, are known from the prior art. Some of these magnets can lift loads of up to 80 tons.
Electromagnets are frequently attached to trolleys, cranes, or similar hoisting mechanisms that then must exert a maximum lifting force composed of the weight of the electromagnets used and the weight to be lifted or load to be transported. For this reason, there has always been an effort to keep the weight of the electromagnets as low as possible, which can be done by selecting the appropriate material, for example aluminum instead of copper.
The problem that, however, remains unsolved is how an emergency power supply can be provided that becomes operative fast enough to prevent the suspended load from dropping in the event of a failure in the line-voltage power system. In terms of the electromagnets considered here that operate on DC power, the first possible solution is a battery that is connected in parallel with the line-voltage power source and is switched on by a switching device when the line voltage drops. Since what must be supplied is relatively high electrical currents over a certain period of time, the resulting battery capacity is high and can only be implemented using a battery of corresponding weight. This weight appears as an additional load which accordingly minimizes the total capacity of the trolley or crane employed.